Hello Supriya

Glad to see that you are interested for UPSC at that age.But i would suggest you to prepare for your 11th and 12th exams because you will get so much time to prepare yourself for UPSC after 12th.Also you have mentioned that you are from Science Stream,that means if you have mathematics as one of your subject it will be beneficial for you because there are many topics where they ask Mathematics questions.

After completing your class 12th,i would suggest you to do BA from any good university like DU,JNU,BHU because this course will help you the most when you prepare for UPSC because there topics is related to History,Polity and Geography which covers almost half of the syllabus for UPSC.

But right now, i want you to focus on you 11th and 12th then go for UPSC because you should have 21 years of age and also graduation degree then only you can give UPSC.

Hope It Helps

Best Of Luck!